The present invention relates to improved dispersant suitable for use as lubricant additives.
Succinimide dispersants of various types are known, including those based on polymer-substituted acylating agents (e.g., succinic anhydrides) prepared by a chlorine-containing alkylation route and those prepared by a so-called “thermal” or non-chlorine alkylation route. Many such dispersants, especially those from the chlorine route have the unwanted effect of leading to an increase in viscosity of lubricant formulations or especially concentrates in which they are included, particularly after the formulation has been allowed to stand for several days to weeks at elevated temperatures. It has now been found that dispersants prepared from a mixture of the chlorine route and the thermal route acylating agents exhibit a significantly reduced level of viscosity increase, compared to those prepared by the chlorine route alone, even when only a relatively small amount of material from the thermal route is present. Such mixtures have the additional benefit of contributing a reduced amount of chlorine to the lubricant to which they are added. Yet another benefit is that the concentrate viscosity of such mixtures of dispersants is lower than that of concentrates of the dispersant from the Cl process alone, leading to improved ease in handling. This improvement is especially significant in concentrate formulations which contain an overbased calcium sulfonate detergent.
Moreover, the present combinations of dispersants can provide a proper balance of seal compatibility, corrosion protection, and antiwear performance required in modern low phosphorus-low sulfur lubricants for heavy duty diesel engines. The proposed reduction of sulfur and phosphorus levels in future diesel oil formulations will necessitate the reduction of the amount of zinc dialkyldithiophosphate (“ZDP”) in the formulation. The reduction of ZDP will be expected to lead to severely reduced antiwear protection of the oil. By using a combination of the dispersants from the chlorine route and the thermal route, as described herein, formulations can be prepared which pass seal compatibility testing (as measured by the MB Viton™ Seal Test), corrosion testing (as measured by the HTCBT test), as well as a wear screening test.
U.S. Pat. No. 5,041,622, LeSuer, Aug. 20, 1991, discloses a process for preparing substituted carboxylic acids useful as acylating agents, reacting an olefin with an acidic reagent such as maleic acid, in the presence of chlorine.
U.S. Pat. No. 6,165,235, Kolp et al., Dec. 26, 2000, U.S. Pat. No. 6,077,909, Pudelski et al., Jun. 20, 2000, disclose acylating agents which are reacted with amines or alcohols to form dispersants having reduced chlorine content.
U.S. Pat. No. 5,719,108, Wilby et al., Feb. 16, 1998, discloses dispersant/VI improvers for lubricating oil composition, comprising the reaction product of a copolymer of octadecene and maleic anhydride with a succinimide prepared from a polyamine and an acyclic hydrocarbyl-substituted succinic anhydride.